Game of Thrones spin-off, here are some key characters who could appear

HBO has begun casting the upcoming Game of Thrones spin-off, House of the Dragon. The project is based on author George RR Martin's Fire & Blood, a history of the House Targaryen, set hundreds of years before the events of GoT.

HBO has committed to 10 episodes of the series, co-created by Ryan Condal and Miguel Sapochnik, who will also direct several episodes. Entertainment Weekly cites sources as saying that the series will, at some point, tackle the famed Targaryen civil war.

Here are some key figures in the story, and their descriptions according to EW. There has been no confirmation about their being a part of the show.

King Viserys I: The beloved fifth Targaryen king whose reign was peaceful and prosperous until his death.

Princess Rhaenyra Targaryen: King Viserys' chosen heir; a dragon rider who grew up expecting to become the first ruling Queen of Westeros.

Queen Alicent Hightower: Viserys' ambitious second wife and Rhaenyra's stepmother, who had three children of her own with the king.

Aegon II Targaryen: Princess Rhaenyra's younger half brother who challenges Rhaenyra's claim to the throne, igniting a civil war.

Previously, another spin-off, created by Jane Goldman, had reached the pilot stage before being axed by HBO. Martin in his blog had written, "It goes without saying that I was saddened to hear the show would not be going to series. Jane Goldman is a terrific screenwriter, and I enjoyed brainstorming with her. I do not know why HBO decided not to go to series on this one, but I do not think it had to do with House of the Dragon."